The present patent application claims the benefit of earlier Japanese Patent Application No. 2000-17483 filed Jan. 26, 2000, the disclosure of which is entirely incorporated herein by reference.
1. Field of the Invention
The present invention relates to a terminal connection structure of a flat circuit belt, such as a flexible flat cable (FFC) or a flexible print-circuit.
2. Description of the Related Art
In general, one or more electric connection terminals are furnished to the end of a flat circuit belt, such as a flat cable, to allow the flat circuit belt to be electrically connected to another circuit. An example of such a connection terminal is disclosed in Japanese Patent Application Laid-open No. 11-144780. FIG. 1 illustrates this type of conventional terminal structure fixed to a flexible flat cable. A conventional connection terminal 3 has a pair of pointed projections 4, which pierce through the conductive film 2 of the flat cable 1 and the insulating layer covering the conductive film 2 all together. The projections 4 are bent inward to form barrels. The penetration of the projections through the conductive film 2 achieves electric connection between the connection terminal 3 and the conductive film 2 of the flat cable 1.
The connection terminal shown in FIG. 1 is generally applied to a wire harness. In this case, the tips of the projections 4 are also caused to pierce through the insulating cover and the conductive film 2 of the flat cable used in the wire harness. The projections 4 sticking out of the top face of the flat cable 1 are then bent inward using a piercing tool so that the tips of the projections 4 dig again into the flat cable, thereby securely holding the flat cable 1.
However, the conventional terminal structure has a problem that the contacts (i.e., the penetrating portion) between the projections 4 and the conductive film 2 has insufficient contact load. For this reason, the contact point or the contact area between the conductive film and the projection easily shifts due to a vibration or a change in temperature. Such unstable contact may cause the contact resistance to increase.
Therefore, it is an object of the invention to reduce the contact fluctuation caused between the conductive film and the projections of a connection terminal, and to provide a terminal structure for a flat circuit belt having a stable contact resistance and reliable electrical characteristics.
To achieve the object, a terminal structure for a flat circuit belt includes a flat circuit belt and a plurality of connection terminals fixed to the end portion of the flat circuit belt. The flat circuit belt comprises multiple conductive strips arranged in parallel to one another at a predetermined interval, and a pair of base films sandwiching the conductive strips. Each connection terminal corresponds to one of the conductive strip. The connection terminal has a contact at its front end, which is to be connected to another contact of a counterpart connector, and a base plate extending from the trailing end of the contact. The base plate has projections facing each other with the base plate between them and piercing through the associated conductive film of the flat circuit belt. The tips of the projections sticking out of the flat circuit belt are bent inward and caulked each other. The feature of the connection terminal is that a groove is formed in the inner face of the projection, so that the conductive film can get into the groove.
The groove allows the contact area between the conductive film and the projection to increase, and at the same time, it prevents the contact between the conductive strip of the flat belt and the connection terminal from shifting. Consequently, stable and reliable electric contact can be achieved.
The flat belt is waved between the facing projections after each projection pierces through the flat belt, with the edges of the conductive film pressed inside the groove. Since a restoration force is caused in the waved conductive film, the contact load between the conductive film and the groove increases, thereby preventing the contact point or contact area from shifting or separating.
The connection terminal also has a pair of bendable retainers on both sides of the projections along the base plate. Each retainer has a pair of walls rising from the base plate and opposed to each other. The walls of the retainer pierce through the base film of the flat circuit belt at both sides of the associated conductive strip.
The retainers positioned before and behind the projections and prevent a stress from affecting the contact between the projections and the conductive film even if the flat circuit belt is pulled strongly. Accordingly, the reliability of the connection between the flat circuit belt and the connection terminal is improved.